Preview of budget AMP vs Purifi based State-Of-The-Art amplifier review

Since audio amplifiers are devices that matters of how cleanly and up to what levels the incoming signal as output, Actual power(but, must be defined in detail) is ultimately everything. We aim to provide useful information for consumer's judgment through numerical reviews, not sensory snake oil, of these factors. 

Please note that this article is a preview of a full review to come, so it does not go into full detail.

Let's see budget amp sample one.

I saw so many recommendations of the Topping PA5 II / Topping PA5 II Plus as decent Hi-Fi stereo amplifier.

But, IMHO it would work fine as a desk amp over extremely short distances, but due to lack of enough power, won't be a true hi-fi amp. 

PA5 II Sample1 with normal power supply
BAL In
4 Ohm 5 W 1 k Hz SINAD - 22.4 kHz
25.0°C (77°F), 55% 

This won't tell anything. This can only indicate that the amplifier is failing or has a serious design flaw. This is the type of measurement you will most likely see on an ASR.
If it's a Normal well designed amp it will just show some meaningless pretty graphs and numbers.

This one looks fine too.

PA5 II Sample1 with normal power supply

BAL In
4 Ohm 5 W 1 k Hz SINAD - Wide band up to 90 kHz
25.0°C (77°F), 55% 

This one also don't tell much. But if amplifier has a design flaw in HF(ultrasound) range we can see. Although this range is not directly audible to the ears, it can create artifacts that extend down into the audible range or cause premature overheating (compression) of speaker tweeters.

And since this information are easily hidden, it's so difficult for consumers to know, and this is the reason why manufacturers who pay attention to even the high-frequency band do not receive the higher evaluation they deserve. Many of brands only care 20-20k narrow band.

Of course, If it's a well designed amp it will just show some meaningless pretty graphs and numbers just as 22.4 kHz.

A slight increase is seen, but it appears to be well suppressed. fine.

Let's see the 4 Ohms Power sweep.

This amp claims 100 W @ 1% THD+N per Ch.
But, we can see protection already triggered around 80 W @ 20 Hz.

Of course, it is a good thing that protection activates before they fried. Some unscrupulous companies produce their products, easily get fried our before protection works, causing permanent physical damage to the product we call the "FRY".

However, since this is a music (wideband high-crest-factor signal) amplifier, not a 1 kHz-only amplifier, the power rating seems bit exaggerated.

Could be rated 80 W, 

If you apply very conservative and strict rules, 65 W (Limiting the range where no significant increase in THD+N is observed at all).

SINAD (Detailed conditions are in the following article)

dB 

Following article, we'll discuss about fine details of each amps and results.
It will include a variety of hard-to-see details, including very high resolution noise level measurements, DC-offset measurements and others what you actually need in real world concern.

Thank you.